JP2020020451A - Manufacturing method of nut of ball screw and manufacturing method of ball screw - Google Patents

Abstract

To provide a manufacturing method of a nut of a ball screw which can easily form a ball circulation groove, and a manufacturing method of the ball screw.SOLUTION: A ball screw comprises a screw shaft having a first screw groove at an external peripheral face, a nut having a second screw groove at an internal peripheral face, and a plurality of balls arranged in a rolling path between the first screw groove and the second screw groove. The nut comprises a ball circulation groove for returning the balls to the other end from one end of the rolling path. A manufacturing method of the nut of the ball screw comprises a forging process for press-pushing a convex die having a curved base bottom face along an internal peripheral face of the nut, and a protrusion protruding from the base bottom face to the internal peripheral face of the nut against the inner peripheral surface of the nut. In the forging process, the base bottom face is higher than a low salient part which is formed along an outer edge of the ball circulation groove, and contacts with four high salient parts which are formed at an end part of the outer edge of the ball circulation groove.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a method for manufacturing a nut of a ball screw and a method for manufacturing a ball screw.

  A ball screw is known as a device for converting a rotary motion into a linear motion. The ball screw includes a screw shaft, a nut, and a plurality of balls. As an example of the ball screw, a ball screw having a concave portion (ball circulation groove) as a path for returning the ball to the inner peripheral surface of the nut is known. The ball circulation groove is formed, for example, by pressing a convex mold having a projection on the outer peripheral surface against the inner peripheral surface of the nut. Patent Documents 1 and 2 disclose an example of a method for manufacturing a nut having a ball circulation groove.

JP 2011-231925 A JP 2013-74664 A

  By the way, when the convex projection is pressed against the inner peripheral surface of the nut, the peripheral portion of the ball circulation groove rises. By pressing the convex protrusion against the inner peripheral surface of the nut, the pressed portion of the nut flows into the constrained relief portion disposed on the outer peripheral surface of the nut. However, there are portions that are difficult to flow due to the convex shape, the distance of the ball circulation groove from the nut end face, or the thickness of the nut. Since the hardly flowing portion rises, the peripheral portion of the ball circulation groove rises. When the outer peripheral surface excluding the convex projection does not contact the inner peripheral surface of the nut when the convex die is at the bottom dead center, the raised portion around the ball circulation groove becomes higher. For this reason, before forming the ball circulation groove arranged on the opposite side of the previously formed ball circulation groove, the raised portion around the previously formed ball circulation groove is cut so that the tool can be inserted into the nut. Need to be kept. On the other hand, when the outer peripheral surface except for the protrusion of the convex shape is in contact with the entire circumference of the raised portion when the convex shape is at the bottom dead center, the convex shape needs to have high strength. Therefore, there is a need for a method of manufacturing a nut that can easily form a ball circulation groove.

  The present invention has been made in view of the above problems, and has as its object to provide a ball screw nut manufacturing method and a ball screw manufacturing method capable of easily forming a ball circulation groove.

  In order to achieve the above object, a method of manufacturing a nut of a ball screw according to a first aspect of the present disclosure includes a screw shaft having a first thread groove on an outer peripheral surface, a nut having a second thread groove on an inner peripheral surface, A plurality of balls disposed in a rolling path between the first screw groove and the second screw groove, wherein the nut returns the ball from one end of the rolling path to the other end. A method for manufacturing a nut of a ball screw having a groove, wherein a convex shape having a curved base surface along the inner peripheral surface of the nut and a projection protruding from the base surface is pressed against the inner peripheral surface of the nut. A forging step, wherein in the forging step, the base surface is higher than a low ridge formed along an outer edge of the ball circulation groove and four heights formed at ends of the outer edge of the ball circulation groove. In contact with the ridge.

  Thereby, since the convex base surface presses the high ridge, the high ridge is reduced. Therefore, between the step of forming the previously formed ball circulation groove and the step of forming the ball circulation groove disposed on the opposite side to the previously formed ball circulation groove, the previously formed ball circulation groove The step of removing the high ridge is not required. Further, since the base surface does not contact the entire periphery of the outer edge of the ball circulation groove, the stress generated in the convex shape is reduced. Therefore, the method of manufacturing the nut of the ball screw can prolong the life of the convex. The ball screw nut manufacturing method can easily form the ball circulation groove.

  As a desirable mode of the method for manufacturing a nut of a ball screw according to the first mode, the convex shape has a curved connection surface connecting the base surface and the projection.

  Accordingly, in the method of manufacturing the nut of the ball screw, sag generated at the boundary between the inner peripheral surface of the nut and the ball circulation groove can be reduced, and breakage of the projection can be suppressed.

  As a desirable mode of the method for manufacturing a nut of a ball screw according to the first aspect, in the forging step, a constraint die is arranged on an outer peripheral surface of the nut, and the constraint die faces a back surface of the ball circulation groove of the nut. Escape part is provided.

  Accordingly, in the method of manufacturing the nut of the ball screw, the sag generated at the boundary between the inner peripheral surface of the nut and the ball circulation groove can be reduced, and the high protruding portion can be further reduced. Further, since the stress generated in the convex is reduced, the method of manufacturing the nut of the ball screw can prolong the life of the convex. Further, since the stress generated in the convex shape is reduced and the height of the high protrusion can be reduced, the radius of curvature of the curved connection surface can be reduced. For this reason, the convex base surface can be widened. As a result, the convex base surface surely presses the high ridge, so that the ball screw nut manufacturing method can easily form the ball circulation groove.

  As a desirable mode of the method of manufacturing the nut of the ball screw of the first aspect, after the forging step, a dripping removing step of removing dripping formed on an outer edge of the ball circulation groove is provided.

  As a result, sag generated at the boundary between the inner peripheral surface of the nut and the ball circulation groove in the forging process is removed. According to the method of manufacturing the nut of the ball screw, the ball is easily scooped into the ball circulation groove. According to the method of manufacturing the nut of the ball screw, the operation of the ball screw can be made smooth.

  As a desirable mode of the ball screw nut manufacturing method of the first mode, the sag removal step is a step of grinding or cutting the inner peripheral surface of the nut.

  Thereby, the sag can be removed more easily in the sag removal step.

  As a desirable mode of the method of manufacturing the nut of the ball screw of the first embodiment, the inner diameter of the nut in the forging step is 0.9 times or more and 1.0 times or more the diameter of a circle which is the locus of the center of the ball in the ball screw. Less than twice.

  Accordingly, the ball screw nut manufacturing method can make the operation of the ball screw smoother.

  As a desirable mode of the method of manufacturing the nut of the ball screw of the first mode, an annealing step of annealing the nut is provided before the forging step.

  Thus, when the convex is pressed against the nut, the nut is likely to be deformed in a desired manner. The ball screw nut manufacturing method can more easily form the ball circulation groove.

  A method of manufacturing a ball screw according to a second aspect of the present disclosure includes a screw shaft having a first screw groove on an outer peripheral surface, a nut having a second screw groove on an inner peripheral surface, the first screw groove, and the second screw. A plurality of balls disposed in a rolling path between the rolling path and the groove, wherein the nut has a ball circulation groove for returning the ball from one end to the other end of the rolling path. A forging step of pressing a convex mold having a curved base surface along the inner peripheral surface of the nut and a projection protruding from the base surface against the inner peripheral surface of the nut, wherein the forging step includes: The surface is higher than the low ridge formed along the outer edge of the ball circulation groove and contacts four high ridges formed at the end of the outer edge of the ball circulation groove.

  Thereby, since the convex base surface presses the high ridge, the high ridge is reduced. Therefore, between the step of forming the previously formed ball circulation groove and the step of forming the ball circulation groove disposed on the opposite side to the previously formed ball circulation groove, the previously formed ball circulation groove The step of removing the high ridge is not required. Further, since the base surface does not contact the entire periphery of the outer edge of the ball circulation groove, the stress generated in the convex shape is reduced. For this reason, the ball screw manufacturing method can extend the life of the convex. The ball screw manufacturing method can easily form the ball circulation groove.

  According to the ball screw nut manufacturing method and the ball screw manufacturing method of the present disclosure, a ball circulation groove can be easily formed.

FIG. 1 is a cross-sectional view of the ball screw according to the embodiment. FIG. 2 is a sectional view of a nut of the ball screw according to the embodiment. FIG. 3 is a flowchart illustrating a method of manufacturing the nut of the ball screw according to the embodiment. Drawing 4 is a mimetic diagram for explaining a forging process of an embodiment. FIG. 5 is a perspective view of a convex shape according to the embodiment. Drawing 6 is a perspective view showing some nuts of an embodiment. FIG. 7 is a sectional view taken along line AA in FIG. FIG. 8 is a sectional view taken along line BB in FIG. FIG. 9 is a sectional view taken along line CC in FIG.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited by the following embodiments for carrying out the invention (hereinafter, referred to as embodiments). The components in the following embodiments include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those that are in the so-called equivalent range. Furthermore, components disclosed in the following embodiments can be appropriately combined. Further, in the following embodiments, the same components as those described above are denoted by the same reference numerals, and overlapping description may be omitted as appropriate.

(Embodiment)
FIG. 1 is a cross-sectional view of the ball screw according to the embodiment. FIG. 2 is a sectional view of a nut of the ball screw according to the embodiment. The ball screw 1 is a device that converts a rotational motion into a linear motion. The ball screw 1 is used for, for example, an electric actuator or the like provided in a vehicle such as an automobile or a motorcycle, a ship, or the like. The ball screw 1 is applied not only to the above-described electric actuator but also to various devices.

  As shown in FIG. 1, a screw shaft 40, a nut 20, and a ball 60 are provided. The screw shaft 40 has a first screw groove 41 on the outer peripheral surface. The first screw groove 41 is a spiral groove. The screw shaft 40 passes through the nut 20. The nut 20 has a second thread groove 21 on the inner peripheral surface. The second screw groove 21 is a spiral groove. The spiral rolling path 11 is formed between the first screw groove 41 and the second screw groove 21. The ball 60 is arranged on the rolling path 11.

  In the following description, the axial direction of the screw shaft 40 and the nut 20 is simply described as the axial direction. A direction perpendicular to the axial direction is simply described as a radial direction. A direction along a circle around the rotation axis Z of the screw shaft 40 and the nut 20 is simply described as a circumferential direction.

  As shown in FIGS. 1 and 2, the nut 20 includes a plurality of ball circulation grooves 23, a first ball circulation groove 23a, a second ball circulation groove 23b, a third ball circulation groove 23c, and a fourth ball circulation groove 23c. And a groove 23d. The number of the ball circulation grooves 23 is not necessarily limited to four and is not particularly limited. The ball circulation groove 23 is a substantially S-shaped groove provided on the inner peripheral surface 25 of the nut 20. The ball circulation groove 23 is a groove that connects one end and the other end of the rolling path 11. The ball circulation groove 23 returns the ball 60 from one end of the rolling path 11 to the other end. When the screw shaft 40 or the nut 20 rotates, the ball 60 circulates infinitely through the rolling path 11 and the ball circulation groove 23.

  As shown in FIGS. 1 and 2, the four ball circulation grooves 23 are arranged at different positions in the axial direction. The four ball circulation grooves 23 are arranged at different positions in the circumferential direction. When viewed from the axial direction, the four ball circulation grooves 23 are arranged at equal intervals in the circumferential direction.

  FIG. 3 is a flowchart illustrating a method of manufacturing the nut of the ball screw according to the embodiment. Drawing 4 is a mimetic diagram for explaining a forging process of an embodiment. FIG. 5 is a perspective view of a convex shape according to the embodiment. Drawing 6 is a perspective view showing some nuts of an embodiment. FIG. 7 is a sectional view taken along line AA in FIG. FIG. 8 is a sectional view taken along line BB in FIG. FIG. 9 is a sectional view taken along line CC in FIG.

  As shown in FIG. 3, the method for manufacturing the nut 20 of the present embodiment includes an annealing step S1 for annealing the nut 20. In the annealing step S1, the nut 20 is heated. The material of the nut 20 is a steel material. For example, the material of the nut 20 is SCM420. The hardness of the nut 20 after the annealing step S1 is not less than HRB60 and not more than HRB90.

  As shown in FIG. 3, the method for manufacturing the nut 20 according to the present embodiment includes a first forging step S2 after the annealing step S1. For example, in the first forging step S2, a first ball circulation groove 23a is formed. As shown in FIG. 4, in the first forging step S <b> 2, the convex 95 is pressed against the inner peripheral surface 25 of the nut 20. The inner diameter D20 of the nut 20 in the first forging step S2 is 0.9 times or more and less than 1.0 times the diameter D60 of the circle (see FIG. 1) which is the locus of the center of the ball 60 in the ball screw 1. The diameter D60 is called BCD (Ball Center Diameter). In the first forging step S2, as shown in FIG. 4, a constraining die 81, a lower die 83, an upper die 85, a case 91, a tool 93, and a convex die 95 are used.

  As shown in FIG. 4, the restraining die 81 is arranged so as to cover the outer peripheral surface 29 of the nut 20. The restraining die 81 restrains the outer peripheral surface 29 of the nut 20. As shown in FIGS. 7 to 9, the constraining die 81 includes an escape portion 813. The escape portion 813 is a groove facing the back surface of the ball circulation groove 23 of the nut 20. The lower mold 83 is arranged so as to cover one end surface of the nut 20. The lower die 83 restrains the lower end surface of the nut 20. The upper die 85 is arranged so as to cover the other end surface of the nut 20. The upper die 85 restrains the upper end surface of the nut 20.

  As shown in FIG. 4, the case 91 is inserted inside the nut 20. The case 91 is cylindrical and has a vertical hole 911 and a horizontal hole 913. The vertical hole 911 is a hole extending from one end surface of the case 91 to the other end surface. The horizontal hole 913 is a hole that connects the outer peripheral surface and the inner peripheral surface of the case 91. The tool 93 is a rod-shaped member, for example, a mandrel. The tool 93 is inserted into the vertical hole 911. The tool 93 has a slope 939 at the end to be inserted into the vertical hole 911.

  As shown in FIG. 4, the convex 95 is disposed in the horizontal hole 913 of the case 91. As shown in FIGS. 4 and 5, the convex 95 has a base surface 951, a protrusion 953, a connection surface 955, and a slope 959. The base surface 951 is a curved surface along the inner peripheral surface 25 of the nut 20. The protrusion 953 protrudes from the base surface 951. The protrusion 953 has a shape corresponding to the ball circulation groove 23. The protrusion 953 is substantially S-shaped. The connection surface 955 is a curved surface connecting the base surface 951 and the projection 953. As shown in FIGS. 7 to 9, in a cross section including the base surface 951 and the protrusion 953, the connection surface 955 draws a curve. The slope 959 is the back surface of the base surface 951. The slope 959 contacts the slope 939 of the tool 93.

  As shown in FIG. 4, in the first forging step S2, the tool 93 moves in the axial direction. When the inclined surface 939 of the tool 93 contacts the inclined surface 959 of the convex 95, the convex 95 moves in the radial direction. When the projection 953 of the convex 95 is pressed against the inner peripheral surface 25 of the nut 20, the inner peripheral surface 25 is plastically deformed. Thereby, the ball circulation groove 23 is formed on the inner peripheral surface 25.

  As shown in FIGS. 7 to 9, in the first forging step S <b> 2, a low protruding portion 26 and a high protruding portion 28 are formed on the outer edge of the ball circulation groove 23 along with the formation of the ball circulation groove 23. The low protrusion 26 is formed along the outer edge of the ball circulation groove 23. The high ridge 28 includes a first high ridge 28a, a second high ridge 28b, a third high ridge 28c, and a fourth high ridge 28d. The first high ridge 28a to the fourth high ridge 28d are higher than the low ridge 26. The first high ridges 28a to the fourth high ridges 28d protrude radially inward from the low ridges 26.

  The first high protrusion 28a is formed at an end Pa (see FIG. 6) in the circumferential direction of the outer edge of the ball circulation groove 23. The second high protrusion 28b is formed at an end Pb (see FIG. 6) of the outer edge of the ball circulation groove 23 in the circumferential direction. The third high protrusion 28c is formed at an end Pc (see FIG. 6) in the circumferential direction of the outer edge of the ball circulation groove 23. The fourth high protrusion 28d is formed at an end Pd (see FIG. 6) in the circumferential direction of the outer edge of the ball circulation groove 23. As shown in FIG. 6, the end Pb is located on the opposite side of the end Pa from the ball circulation groove 23. The end Pd is a position opposite to the end Pc with the ball circulation groove 23 interposed therebetween. The low protrusion 26 is formed on the outer edge of the ball circulation groove 23 excluding the end Pa, the end Pb, the end Pc, and the end Pd.

  7 to 9 show the nut 20, the constraint mold 81 and the convex mold 95 when the tool 93 (see FIG. 4) is at the bottom dead center. As shown in FIG. 7, when the tool 93 is at the bottom dead center, the base surface 951 of the convex 95 does not contact the low ridge 26. When the tool 93 is at the bottom dead center, there is a gap between the base surface 951 of the convex 95 and the low ridge 26. As shown in FIGS. 8 and 9, when the tool 93 is at the bottom dead center, the base surface 951 of the convex 95 has the first high ridge 28 a, the second high ridge 28 b, the third high ridge 28 c, It contacts the fourth high ridge 28d. That is, when the tool 93 is at the bottom dead center, the base surface 951 of the convex 95 contacts the four high ridges 28.

  As shown in FIGS. 7 to 9, with the formation of the ball circulation groove 23 in the first forging step S <b> 2, the back surface of the ball circulation groove 23 of the nut 20 projects toward the escape portion 813. The volume of the escape portion 813 is larger than the volume of the protrusion formed on the back surface of the ball circulation groove 23 of the nut 20.

  As shown in FIG. 3, the method for manufacturing the nut 20 of the present embodiment includes a second forging step S3 after the first forging step S2. For example, in the second forging step S3, a second ball circulation groove 23b is formed. As shown in FIG. 4, in the second forging step S <b> 3, the convex 95 is pressed against the inner peripheral surface 25 of the nut 20. In the second forging step S3, similarly to the first forging step S2, when the tool 93 is at the bottom dead center, the base surface 951 of the convex 95 contacts the four high ridges 28.

  As shown in FIG. 3, the method for manufacturing the nut 20 of the present embodiment includes a third forging step S4 after the second forging step S3. For example, in the third forging step S4, a third ball circulation groove 23c is formed. As shown in FIG. 4, the convex 95 is pressed against the inner peripheral surface 25 of the nut 20 in the third forging step S4. In the third forging step S4, similarly to the first forging step S2, when the tool 93 is at the bottom dead center, the base surface 951 of the convex 95 contacts the four high ridges 28.

  If the base surface 951 of the convex 95 does not contact the high ridge 28 in the first forging step S2, the height of the high ridge 28 around the first ball circulation groove 23a becomes higher. In this case, if the tool 93 is moved in the axial direction in the third forging step S4, the tool 93 may interfere with the high protrusion 28 of the first ball circulation groove 23a. For this reason, before the third forging step S4, a step of removing the high protrusion 28 is required. On the other hand, in the present embodiment, as described above, in the first forging step S2, the base surface 951 of the convex die 95 is in contact with the high ridge 28, so that the height of the high ridge 28 around the first ball circulation groove 23a is high. Is reduced. Thereby, it is possible to proceed to the third forging step S4 without passing through the step of removing the high raised portion 28.

  As shown in FIG. 3, the method for manufacturing the nut 20 according to the present embodiment includes a fourth forging step S5 after the third forging step S4. For example, in the fourth forging step S5, a fourth ball circulation groove 23d is formed. As shown in FIG. 4, in the fourth forging step S <b> 5, the convex 95 is pressed against the inner peripheral surface 25 of the nut 20. In the fourth forging step S5, similarly to the first forging step S2, when the tool 93 is at the bottom dead center, the base surface 951 of the convex 95 contacts the four high ridges 28.

  If the base surface 951 of the convex 95 does not contact the high ridge 28 in the second forging step S3, the high ridge 28 around the second ball circulation groove 23b becomes higher. In this case, if the tool 93 is moved in the axial direction in the fourth forging step S5, the tool 93 may interfere with the high protrusion 28 of the second ball circulation groove 23b. For this reason, before the fourth forging step S5, a step of removing the high protrusion 28 is required. On the other hand, in the present embodiment, as described above, in the second forging step S3, the base surface 951 of the convex die 95 is in contact with the high ridge 28, so that the height of the high ridge 28 around the second ball circulation groove 23b is high. Is reduced. Thereby, it is possible to proceed to the fourth forging step S5 without passing through the step of removing the high raised portion 28.

  As shown in FIG. 3, the method for manufacturing the nut 20 of the present embodiment includes, after the fourth forging step S <b> 5, a sag removing step S <b> 6 for removing the sag 27 formed on the outer edge of the ball circulation groove 23. In the present embodiment, the sag removal step S6 is a step of grinding or cutting a part or the entire circumference of the inner peripheral surface 25 of the nut 20. The sag removal step S6 is performed after all the ball circulation grooves 23 have been formed. In the sagging removal step S6, the inner peripheral surface 25 of the nut 20 is ground or cut so that all the sagging 27 is removed. The sag 27 is a curved corner formed at the boundary between the inner peripheral surface 25 and the ball circulation groove 23 when the convex 95 is pressed against the inner peripheral surface 25 of the nut 20. For example, in the sagging removal step S6, the inner peripheral surface of the nut 20 is ground or cut along the line L shown in FIGS.

  After the sag removal step S6, the second thread groove 21 is formed on the inner peripheral surface 25 of the nut 20 by, for example, cutting. Thereby, the nut 20 shown in FIG. 2 is formed.

  After manufacturing the nut 20, the ball screw 1 is manufactured. The method of manufacturing the ball screw 1 according to the present embodiment includes an assembling step of assembling the nut 20, the screw shaft 40, and the ball 60 after manufacturing the nut 20.

  In the method of manufacturing the nut 20, the first ball circulation groove 23a, the second ball circulation groove 23b, the third ball circulation groove 23c, and the fourth ball circulation groove 23d are not necessarily formed in this order. The order of forming the plurality of ball circulation grooves 23 is not particularly limited. For example, in the first forging step S2, the second ball circulation groove 23b, the third ball circulation groove 23c, or the fourth ball circulation groove 23d may be formed.

  The method of manufacturing the nut 20 does not necessarily have to include the four forging steps (the first forging step S2 to the fourth forging step S5). The method of manufacturing the nut 20 may include at least one forging step.

  As described above, the ball screw 1 includes the screw shaft 40 having the first screw groove 41 on the outer peripheral surface, the nut 20 having the second screw groove 21 on the inner peripheral surface, the first screw groove 41 and the second screw groove. A plurality of balls 60 arranged in the rolling path 11 between the thread groove 21 and the thread groove 21. The nut 20 includes a ball circulation groove 23 that returns the ball 60 from one end of the rolling path 11 to the other end. The method of manufacturing the nut 20 of the ball screw 1 is as follows: the convex mold 95 having the curved base surface 951 along the inner peripheral surface 25 of the nut 20 and the projection 953 protruding from the base surface 951 is formed on the inner peripheral surface 25 of the nut 20. (A first forging step S2, a second forging step S3, a third forging step S4, and a fourth forging step S5). In the forging process, the base surface 951 is higher than the low protruding portion 26 formed along the outer edge of the ball circulation groove 23 and contacts the four high protruding portions 28 formed at the end of the outer edge of the ball circulation groove 23. .

  As a result, the base surface 951 of the convex 95 presses the high ridge 28, so that the high ridge 28 is lowered. For this reason, between the step of forming the previously formed ball circulation groove 23 and the step of forming the ball circulation groove 23 disposed on the opposite side to the previously formed ball circulation groove 23, the first step is performed. The step of removing the high protrusion 28 of the ball circulation groove 23 becomes unnecessary. Further, since the base surface 951 does not contact the entire periphery of the outer edge of the ball circulation groove 23, the stress generated in the convex 95 is reduced. For this reason, the manufacturing method of the nut 20 of the ball screw 1 can extend the life of the convex 95. The method of manufacturing the nut 20 of the ball screw 1 can easily form the ball circulation groove 23.

  In the method of manufacturing the nut 20 of the ball screw 1, the convex 95 has a curved connection surface 955 that connects the base surface 951 and the projection 953.

  Accordingly, in the method of manufacturing the nut 20 of the ball screw 1, sag occurring at the boundary between the inner peripheral surface 25 of the nut 20 and the ball circulation groove 23 can be reduced, and breakage of the projection 953 can be suppressed.

  In the forging step (first forging step S2, second forging step S3, third forging step S4, and fourth forging step S5), the constraining die 81 is arranged on the outer peripheral surface 29 of the nut 20. The constraining die 81 includes a relief portion 813 facing the back surface of the ball circulation groove 23 of the nut 20.

  Accordingly, in the method of manufacturing the nut 20 of the ball screw 1, the sag generated at the boundary between the inner peripheral surface 25 of the nut 20 and the ball circulation groove 23 can be reduced, and the height of the high protrusion 28 can be further reduced. In addition, since the stress generated in the convex 95 is reduced, the method of manufacturing the nut 20 of the ball screw 1 can extend the life of the convex 95. Further, since the stress generated in the convex 95 is reduced and the height of the high protrusion 28 can be reduced, the radius of curvature of the curved connection surface 955 can be reduced. For this reason, the base surface 951 of the convex 95 can be widened. As a result, the base surface 951 of the projection 95 reliably presses the high ridge 28, so that the method of manufacturing the nut 20 of the ball screw 1 can easily form the ball circulation groove 23.

  The method of manufacturing the nut 20 of the ball screw 1 is such that the nut 20 is formed on the outer edge of the ball circulation groove 23 after the forging step (first forging step S2, second forging step S3, third forging step S4, and fourth forging step S5). And a sag removing step S6 for removing sagging 27.

  As a result, sag generated at the boundary between the inner peripheral surface 25 of the nut 20 and the ball circulation groove 23 in the forging process is removed. According to the method of manufacturing the nut 20 of the ball screw 1, the ball 60 is easily scooped into the ball circulation groove 23. According to the method of manufacturing the nut 20 of the ball screw 1, the operation of the ball screw 1 can be made smooth.

  In the method of manufacturing the nut 20 of the ball screw 1, the sag removal step S6 is a step of grinding or cutting the inner peripheral surface of the nut 20.

  Thereby, the sag 27 can be more easily removed in the sag removing step S6.

  The inner diameter D20 (see FIG. 4) of the nut 20 in the forging process (first forging process S2, second forging process S3, third forging process S4, and fourth forging process S5) is the locus of the center of the ball 60 in the ball screw 1 Is 0.9 times or more and less than 1.0 times the diameter D60 of the circle (see FIG. 1).

  Thereby, the method of manufacturing the nut 20 of the ball screw 1 can make the operation of the ball screw 1 smoother.

  The method of manufacturing the nut 20 of the ball screw 1 includes an annealing step S1 of annealing the nut 20 before the forging step (first forging step S2, second forging step S3, third forging step S4, and fourth forging step S5). Is provided.

  Thereby, when the convex mold 95 is pressed against the nut 20, desired deformation of the nut 20 is likely to occur. The method of manufacturing the nut 20 of the ball screw 1 allows the ball circulation groove 23 to be formed more easily.

  The method of manufacturing the ball screw 1 is such that the convex 95 having a curved base surface 951 along the inner peripheral surface 25 of the nut 20 and a projection 953 protruding from the base surface 951 is pressed against the inner peripheral surface 25 of the nut 20. Steps (first forging step S2, second forging step S3, third forging step S4, and fourth forging step S5) are provided. In the forging process, the base surface 951 is higher than the low protruding portion 26 formed along the outer edge of the ball circulation groove 23 and contacts the four high protruding portions 28 formed at the end of the outer edge of the ball circulation groove 23. .

  As a result, the base surface 951 of the convex 95 presses the high ridge 28, so that the high ridge 28 is lowered. For this reason, between the step of forming the previously formed ball circulation groove 23 and the step of forming the ball circulation groove 23 disposed on the opposite side to the previously formed ball circulation groove 23, the first step is performed. The step of removing the high protrusion 28 of the ball circulation groove 23 becomes unnecessary. Further, since the base surface 951 does not contact the entire periphery of the outer edge of the ball circulation groove 23, the stress generated in the convex 95 is reduced. For this reason, the manufacturing method of the ball screw 1 can prolong the life of the convex 95. In the method of manufacturing the ball screw 1, the ball circulation groove 23 can be easily formed.

Reference Signs List 1 ball screw 11 rolling path 20 nut 21 second screw groove 23 ball circulation groove 25 inner peripheral surface 26 low protruding portion 27 sag 28 high protruding portion 28a first high protruding portion 28b second high protruding portion 28c third high protruding portion 28d Fourth raised portion 40 Screw shaft 41 First screw groove 60 Ball 81 Restricted type 813 Escape portion 83 Lower die 85 Upper die 91 Case 911 Vertical hole 913 Lateral hole 93 Tool 939 Beveled surface 95 Convex type 951 Base surface 953 Projection 955 Connection surface 959 Slope D20 Inner diameter D60 Diameter L Line Pa, Pb, Pc, Pd End S1 Annealing step S2 First forging step S3 Second forging step S4 Third forging step S5 Fourth forging step S6 Sag removal step Z Rotary shaft

Claims (8)

A screw shaft having a first screw groove on an outer peripheral surface, a nut having a second screw groove on an inner peripheral surface, and a plurality of nuts arranged on a rolling path between the first screw groove and the second screw groove. A ball, comprising: a ball circulation groove that returns the ball from one end of the rolling path to the other end;
A forging step of pressing a convex mold having a curved basal surface along the inner peripheral surface of the nut and a projection protruding from the basal surface against the inner peripheral surface of the nut,
In the forging step, the base surface is higher than a low protruding portion formed along the outer edge of the ball circulation groove, and is in contact with four high protuberances formed at ends of the outer edge of the ball circulation groove. Manufacturing method of screw nut. The method for manufacturing a nut for a ball screw according to claim 1, wherein the protrusion has a curved connection surface that connects the base surface and the protrusion. In the forging process, a restraining die is arranged on an outer peripheral surface of the nut,
The method of manufacturing a nut for a ball screw according to claim 1, wherein the restraining type includes a relief portion facing a back surface of the ball circulation groove of the nut. The method for manufacturing a nut of a ball screw according to any one of claims 1 to 3, further comprising a sag removing step of removing sagging formed on an outer edge of the ball circulation groove after the forging step. The method for manufacturing a nut for a ball screw according to claim 4, wherein the sagging removal step is a step of grinding or cutting an inner peripheral surface of the nut. The nut of the ball screw according to claim 4 or 5, wherein an inner diameter of the nut in the forging step is 0.9 times or more and less than 1.0 times a diameter of a circle which is a locus of a center of the ball in the ball screw. Manufacturing method. The method of manufacturing a nut for a ball screw according to any one of claims 1 to 6, further comprising an annealing step of annealing the nut before the forging step. A screw shaft having a first screw groove on an outer peripheral surface, a nut having a second screw groove on an inner peripheral surface, and a plurality of nuts arranged on a rolling path between the first screw groove and the second screw groove. And a ball, wherein the nut is a ball screw manufacturing method including a ball circulation groove for returning the ball from one end of the rolling path to the other end,
A forging step of pressing a convex mold having a curved basal surface along the inner peripheral surface of the nut and a projection protruding from the basal surface against the inner peripheral surface of the nut,
In the forging step, the base surface is higher than a low protruding portion formed along the outer edge of the ball circulation groove, and is in contact with four high protuberances formed at ends of the outer edge of the ball circulation groove. Screw manufacturing method.

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